The present invention relates generally to ocean thermal energy conversion power systems, and more particularly, to a method and apparatus for transferring cold water maintained adjacent the lower depths of the ocean upward toward the upper region of the ocean to increase the efficiency of ocean thermal energy conversion systems.
With the world energy demand continuing to increase at an exponential rate, and known petroleum reserves being rapidly deplenished, attention has been directed to the utilization and development of alternative non-conventional energy sources. Much of this attention has been directed toward ocean bodies which, due to their immense size (covering nearly three-quarters of the earth's surface) and their ability to naturally store substantial quantities of solar radiation, represent a vast energy source potential. Although tidal water conversion systems have recently been utilized in some ocean bodies, to date the most promising means for extracting energy from the ocean appears to be ocean thermal energy conversion systems.
Basically, such ocean thermal energy conversion systems utilize a heat cycle or Carnot engine which operates on the temperature differential or thermal gradient existing between the ocean's surface and its lower depths, which typically is a magnitude of approximately 20 degrees Celsius. Due to this temperature gradient, a suitable working fluid, such as ammonia, Freon, and/or water, may be selectively vaporized by the warm upper region seawater and expanded through a turbine to yield a direct mechanical power output or alternatively, coupled to a generator to produce an electrical power output. Subsequent to the expansion of the vaporized working fluid through the turbine, cold water from the lower depths of the ocean may be utilized to condense the working fluid vapor, with the evaporation, turbine expansion, and condensing processes being repeated on a continuous basis. As is well known, the maximum efficiency of such heat cycle engines or Carnot engine systems is a function of the absolute temperature gradient existing between the evaporator and condenser of the engine. With specific reference to ocean thermal energy conversion systems, the maximum thermal efficiency is equal to ##EQU1## which, typically, is approximately 7 to 9 percent.
Due to the maximum thermal efficiency of the ocean thermal energy conversion plants being limited to this low percentage, to produce a net power gain during operation, the auxilary systems, such as the turbine, electrical generator, and pumping systems, must be designed to operate at extremely high efficiencies. Although the state-of-the-art turbine and electrical generator design has, to a great extent, reached such high efficiencies, the necessity of pumping large quantities of cold water from ocean depths approximating 2,000 to 3,000 feet has placed a severe energy drain on the ocean thermal power plants. This pumping inefficiency has been the major limitation on ocean thermal energy conversion systems and, in many cases, has reduced the overall system efficiency to as low as 1 or 2 percent. As such, there exists substantial need for a high efficiency apparatus and method for transporting cold water from the lower ocean depths upward toward the ocean thermal power plant.